The control of cell proliferation is a central event in tumorigenesis and often depends on the interactions between growth factors and their specific receptor-activated signaling pathways. The nature of the local extracellular matrix modulates cellular responses to a given signal via various means, for example by affecting the affinity of the ligand for its cognate receptor and by influencing proteolytic processing and internalization (lozzo, R. V. and A. D. Murdoch. 1996. FASEB J. 10:598-614).
There is increasing evidence that decorin (Krusius, T. and E. Ruoslahti. 1986. Proc. Natl. Acad. Sci. USA 83:7683-7687; Day, A. A. et al. 1987. Biochem. J. 248:801-805; Fisher, L. W. et al. 1989. J. Biol. Chem. 264:4571-4576), a member of an expanding gene family encoding small leucine-rich proteoglycans, plays an role in modulating cell proliferation, cell adhesion, cell migration, and collagen fibril formation. Decorin can bind in vitro to a variety of adhesive and nonadhesive proteins including fibronectin, thrombospondin, various types of collagens, and transforming growth factor-xcex2 (TGF-xcex2; lozzo, R. V. and A. D. Murdoch. 1996. FASEB J. 10:598-614). The binding of decorin to fibrillar collagen carries important biological implications as recently demonstrated by the phenotype of mice lacking the decorin gene (Danielson, K. G. et al. 1997. J. Cell Biol. 136:729-743). In these mutant animals, disruption of the decorin gene leads to skin fragility and abnormal collagen morphology, characterized by uncontrolled lateral fusion of fibrils. Binding of decorin to TGF-xcex2 prevents fibrosis of renal glomeruli by neutralizing its biological activity (Border, W. A. et al. 1992. Nature 360:361-364). Decorin cDNA was recently used as a gene therapy tool for treatment of fibrotic diseases caused by TGF-xcex2 (Isaka, Y. et al. 1996. Nat. Med. 2:418-423).
Decorin has also been implicated in the control of cell proliferation. Forced expression of decorin in Chinese hamster ovary (CHO) cells has been demonstrated to lead to decreased growth rate, lowered saturation density, and altered morphology (Yamaguichi, Y. and R. Ruoslahti. 1988. Nature 336:244-246). It has been suggested that decorin causes these changes in this cell system by sequestering TGF-xcex2, an autocrine growth stimulator for these cells (Yamaguichi, Y. et al. 1990. Nature 346:281-284). Decorin is also markedly upregulated during quiescence in human diploid fibroblasts (Coppock, D. L. et al. 1993. Cell Growth Differ. 4:483493; Mauviel, A. et al. 1995. J. Biol. Chem. 270:11692-11700) and its expression is strongly suppressed upon viral transformation with SV40 (Coppock, D. L. et al. 1993. Cell Growth Differ. 4:483-493). Decorin is rarely expressed by malignant epithelial cells from a wide variety of human tumors including colon, pancreas, prostate, and breast carcinomas (lozzo, R. V. and I. Cohen. 1993. Experientia 49:447-455). However, in the tumor stoma of colon cancer, the amount of decorin proteoglycan is increased markedly through a process that involves hypomethylation of the decorin gene (Adany, R. et al. 1990. J. Biol. Chem. 265:11389-11396) as well as induction of this gene product via tumor-secreted cytokines (lozzo, R. V. 1985. J. Biol. Chem. 260:7464-7473).
Using a gene transfer approach in human colon carcinoma cells that do not constitutively express this gene, it was demonstrated that de novo expression of decorin reverted the cells to a normal phenotype. In these experiments, the cells lost anchorage-independent growth, failed to generate tumors in scid/scid mice, and became arrested in the G1 phase of the cell cycle (Santra, M. et al. 1995. Proc. Nati. Acad. Sci. USA 92:7016-7020). This decorin-induced growth arrest was associated with a marked induction of p21Waf1/cip1/sdi1 (p21), a potent inhibitor of cyclin-dependent kinase (CDK) activity (Harper, J. W. et al. 1993. Cell 75:805-816; El-Deiry, W. S. et al. 1993. Cell 75:817-825). Experiments also have shown that augmented p21 protein is present in a multimeric complex with various cyclins and CDKs in the nuclei of decorin-expressing clones and that its levels can be abolished by abrogating decorin expression (DeLuca, A. et al. 1996. J. Biol. Chem. 271:18961-18965).
It has now been found that administration of decorin to tumor cells results in suppression of the growth of tumor cells.
The present invention provides a method for suppressing tumor growth by administration of decorin, a proteoglycan.
According to one embodiment, a method for suppressing tumor cell growth in an animal comprises administering to an animal suffering from a tumor a decorin gene protein product so that tumor growth is suppressed in the animal. According to one preferred embodiment, the decorin gene product comprises wild-type decorin or xcex94decorin. The decorin gene product is administered systemically according to one embodiment, and locally, to the tumor site, in other embodiments.
According to another embodiment, a method for suppressing tumor cell growth in an animal comprises administering to an animal suffering from a tumor a vector expressing a decorin gene protein product so that tumor growth is suppressed in the animal. According to one preferred embodiment, the vector expresses wild-type decorin gene product or xcex94decorin. The vector is preferably a retroviral vector or an adenoviral vector.
In one embodiment, the vector is administered to cells of the patient in vivo, either systemically or locally to the tumor site. According to another embodiment, the vector is administered to normal cells of the patient ex vivo to obtain over-expression of the decorin protein gene product by such cells. The cells are then returned to the body of the patient in the vicinity of the tumor.
According to one preferred embodiment, the tumor cells subject to treatment express epidermal growth factor receptors. According to another preferred embodiment, the tumor is characterized by a deleterious p53 mutation.
The animal treated according to the present invention is preferably a human being.